1. Field of the Invention
This invention relates to a light source module comprising a light source, an optical waveguide and an inlet optical system for coupling light emitted from the light source to one end of the optical waveguide.
2. Description of the Related Art
There has been well known a light source module comprising a semiconductor laser and an inlet optical system for coupling light emitted from the semiconductor laser to a light inlet end face of an optical fiber as an optical communication component. In the inside of the light source module, the inlet optical system and the optical fiber are fixed together with an adhesive means such as solder or adhesive in order to stably keep the semiconductor laser coupled to the light inlet end face of the optical fiber in the order of micro meters.
In such an optical module, the package accommodating therein the light source module is generally hermetically sealed in order to prevent deterioration of the laser by humidity of the atmosphere. For example, the structure represented by the CAN package is representative of a sealing structure for protecting a semiconductor laser or an end face of a laser. In such a light source module, there has been a problem that pollutant remaining in the hermetically sealed package can adhere to an optical component such as a light outlet end face of the laser, the inlet optical system or the optical fiber to deteriorate the laser properties. Especially, the pollutant adheres more where is high in optical density. (dust collection effect) Such dust collection effect is more remarkable in light source modules comprising, for instance, a GaN semiconductor laser which radiates a laser beam in the range of 350 to 500 nm (400 nm band) since in such light source modules, photon energy is high and a photochemical reaction with material is apt to occur.
As a pollutant, for instance, hydrocarbon compound mixed therein from the atmosphere of a producing step can be included, and there has been known a fact that material polymerized or decomposed by the laser beam adheres to the hydrocarbon compound to prevent improvement in optical output.
In Japanese Unexamined Patent Publication No. 2004-179595, there has been disclosed a technology where, in order to suppress pollution of the light inlet end face of the optical fiber, the light inlet end face of the optical fiber is coated with a photo-catalyst such as titanium oxide film active to laser beams and/or nitrogen-doped titanium oxide film. Further, in Japanese Unexamined Patent Publication No. 2004-253783, there has been disclosed a technology where a transparent body such as a glass block is brought into close contact with the light inlet end face of the optical fiber to protect the light inlet end face of the optical fiber. Further, in Japanese Unexamined Patent Publication No. 2004-252425, there has been disclosed a technology where the light inlet end face of the optical fiber is brought into close contact with the outside of the window of the package to suppress adhesion of the pollutant to the light inlet end face of the optical fiber.
As described above, the package of a precision optical component such as a semiconductor laser or an optical fiber is hermetically sealed in order to protect the precision optical component from pollutant. However, since the package for hermetically sealing each of optical systems which are variously shaped are not for a wide use and accordingly must be ordered for each optical system, whereby cost of thousands to tens of thousands of yens is required which adds to the cost of light source modules.